Superconduction is a phenomenon to make a resistance value completely zero, which was found using mercury by Dutch Kamerring Onnes who developed a freezer. Subsequently, a superconducting transition temperature (Tc) was defined as 39 K by Bardeen Cooper Schrieffer (BCS) theory, but this was Tc of a first type superconductor.
In a second type superconductor found by Bednorz or the like in 1986, a result better than 39 K was indicated, leading to development of an oxide superconductor which can be used at a liquid nitrogen temperature. The oxide superconductor is a second type superconductor in which a superconducting state and a non-superconducting state are mixed. At present, many high temperature oxide superconductors which can be used at a liquid nitrogen temperature are on sale in a lot of 500 m. Application of a superconducting wire is expected to various large apparatuses such as a superconducting power transmission cable, a nuclear fusion furnace, a magnetically levitated train, a particle accelerator, and a magnetic diagnostic apparatus (MRI).
Typical examples of a developed high temperature oxide superconductor include a bismuth-based superconducting wire called a first generation and an yttrium-based superconducting wire called a second generation. Manufacturing withdrawal of the first generation requiring silver in an amount of 60% by volume or more has occurred successively, and extremely a few companies manufacture the first generation now in the world.
On the other hand, a total sold wire length of the second generation in which a substrate is inexpensive and a physical strength is excellent is more than 3,000 km. A 50 MVA DC power transmission cable system manufactured using a large amount of wire materials had an operation achievement result of three years or more at the point of August 2015. Since September 2014, a DC power transmission cable system having a capacity of 500 MVA has been operated. A power transmission capacity of 500 MVA corresponds to power of approximately 50% of a standard nuclear reactor.
The wire material has been sold in a total length of 3,000 km or more. A large contract of 20 km or more in a wire length, delivery thereof, and an application achievement result thereof all used wire materials manufactured by a metal organic deposition using trifluoroacetates (TFA-MOD) method. The TFA-MOD method is a first manufacturing method which manufactures a wire material having a length of 500 m stably, can supply the wire material in a large amount, and has an application achievement result. Typical examples of another second generation manufacturing method include a pulsed laser deposition (PLD) method and a metal organic chemical vapor deposition (MOCVD) method. However, both of the methods have a problem in composition control, and have not achieved stable mass production of a wire material having a length of 500 m at present. Therefore, at present, the wire material manufactured by the TFA-MOD method has a wire material share of approximately 100%.
This fact does not deny future of the PLD method or the MOCVD method. A manufacturing method using physical deposition has difficulty in composition control. However, if a technique capable of controlling three kinds of elements flying in vacuum and having a difference of twice or more relative to one another in an atomic weight so as to have a composition difference of 1% or less at almost the same level as the TFA-MOD method using an inexpensive method is developed, mass production is possible. However, this problem has not been solved for 28 years or more since 1987.
Meanwhile, wire materials manufactured by the PLD method or the MOCVD method are leading in coil application requiring a magnetic field characteristic. This is because an artificial pin required for improving a magnetic field characteristic is easily introduced. However, a coil manufactured by using a superconducting wire manufactured by the PLD method or the MOCVD method has no satisfactory achievement result at present. The manufacturing number thereof is considered to be 20 to 30. However, it does not seem that completion of a satisfactory coil has been reported.